2010 MBP Won't Boot!

Hey guys,
I have a 2010 MacBook Pro 2.6Ghz i7
I have been running Snow Leopard since I got it and I refuse to use Lion. (For many a reason.)

Me trying to have a contingency plan, made a second boot drive. Which was useful because my original drive had crashed later and I put the backup into my MBP and booted from it and was back up and running in minutes. It was fantastic.

The second hard drive that I had was a tiny 160GB so I knew I would need to buy a new 500GB at some point to move back to, and that is what I just did and now I am having issues. I bought a Seagate Momentus XT drive. (500GB with 4GB of solid state memory.) I don't believe the issue is with the drive, but I will get to that soon enough.

I tried to boot my MBP from a retail version of SL and (using verbose mode) I watch it try to boot until it gets stuck at the what I believe is the Kernel. It will not progress any farther even if I let it sit for hours. I tried to boot from the SL disk on my MBP, a co-workers Lion MBP, and a Lion iMac. None of them would boot the from the disk. So I thought that maybe Apple was being Apple and would no longer support booting from SL disks. (A ploy to get you to move to lion maybe?) So I found a SL iMac at work and I booted from the disk on there and installed SL on my hard drive from an external firewire enclosure. It installed SL successfully and I was able to boot the iMac from the hard drive I just installed SL on. (Which is why I don't believe the Momentus XT drive is bad.)

Then when I put the hard drive back into my MBP I would boot my computer (using Verbose mode) and would watch it get stuck at a similar spot that the SL disk would get caught up on. It would not boot and I am completely clueless on what is wrong.

If I put the 160GB hdd into the MBP and boot the computer it will be perfectly fine and boot successfully. Additionally I have tried booting the computer with the 160GB drive and installing SL on to my new drive but that didn't work either. I'll try with a USB copy of SL tomorrow but until then I am baffled.

Any suggestions on what I need to do or what the issue is????

 

I didn't update it on the iMac. I will definitely try that tomorrow and see if it helps.
It wouldn't be that the OS is hardware specific to an iMac v MBP? Like a compilation difference.